Environmental pollution concerns have led those in the coatings and resins arts to develop curable compositions from which organic solvents have been eliminated or at least substantially reduced. Moreover, the high cost and scarcity of petroleum by-products has generated interest in the development of curable compositions based entirely, or at least substantially, on inorganic components.
Inorganic coating compositions based on alkali metal silicates and inorganic phosphate hardeners are known. However, when alkali metal silicates and inorganic phosphate hardeners are mixed, they tend to rapidly coagulate, solidify or the like due to the strong reactivity between the silicate and the phosphate. Thus compositions based on alkali metal silicates and metal phosphate hardeners tend to have relatively short useful lives. Additionally, due to this strong reactivity, generally known alkali silicate/phosphate hardener compositions generally contain undesirable particles or lumps. Such particles or lumps interfere, for example, in spraying applications employing compositions containing these particles or lumps. Furthermore, cured coatings produced from such compositions contain highly undesirable lumps.
Applicants' copending application Ser. No. 218,861 filed Dec. 22, 1980 discloses an aqueous curable composition containing an alkali metal silicate and an aqueous dispersion of a metal condensed phosphate hardener containing an amount of base sufficient to raise the pH of the hardener dispersion to a value greater than 9.5. Such compositions containing the specified amount of base cure to smooth, essentially lump-free, durable coatings.
The present invention is directed to curable inorganic coating compositions based on water-soluble and/or water-dispersible alkali metal silicates which have extended useful lives. Further objects of the present invention will become apparent in the description of the invention.